labs-vagrant: add git-update command
labs-vagrant: add git-update command

S pointed out that this was missing in an email.

Change-Id: I30a3b776934e3aba5e4be43b95fc7435a1d12a80

ankita-kumari/mediawiki-vagrant,HarriAlasi/wiki3dviewer,ankita-kumari/mediawiki-vagrant,HarriAlasi/wiki3dviewer,stuartbman/mediawiki-vagrant,ankita-kumari/mediawiki-vagrant,stuartbman/mediawiki-vagrant,wikimedia/mediawiki-vagrant,HarriAlasi/wiki3dviewer,HarriAlasi/wiki3dviewer,stuartbman/mediawiki-vagrant,HarriAlasi/wiki3dviewer,stuartbman/mediawiki-vagrant,ankita-kumari/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,stuartbman/mediawiki-vagrant,ankita-kumari/mediawiki-vagrant,ankita-kumari/mediawiki-vagrant,stuartbman/mediawiki-vagrant,HarriAlasi/wiki3dviewer,wikimedia/mediawiki-vagrant,HarriAlasi/wiki3dviewer,stuartbman/mediawiki-vagrant,wikimedia/mediawiki-vagrant